In a large mixing bowl, cream the butter and the sugar on high until it is fluffy and there are no more lumps. Break apart any chunks of butter or sugar with a fork and scrape down the sides of the bowl.

Add the vanilla extract and the sour cream and mix on a low setting. Then add in the eggs and mix on low until just incorporated. Do not overmix.

Add in the baking soda, cornstarch, salt, and just one cup of the all purpose flour then mix on low. Slowly add in the rest of the flour one cup at a time and mix until there are no more streaks of flour in the dough.

Divide the dough evenly into three separate bowls and add a few drops of the gel food coloring at a time. Mix it all in with a spatula or spoon. Add more food coloring as needed until the desired color is achieved. Keep in mind that the cookies will lighten a bit as they bake. Then cover the bowls in plastic wrap and place in the refrigerator to chill for at least 30 minutes. The dough will be very sticky but will be firmer and easier to work with after chilling.

Scoop about half a tablespoon of each color of the dough and roll them into individual balls (about 1 inch in diameter). Then grab one of each color ball and push them together and carefully roll them into one larger ball.

Place each ball about 4 inches apart and lightly flatten them into a small cookie shape with your fingers. They will continue to spread and rise as they bake so make sure they have enough space between them.